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Restore some code
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@fingolfin
fingolfin committed Jun 20, 2024
1 parent 01c2703 commit 3847eb7
Showing 1 changed file with 45 additions and 25 deletions.
70 changes: 45 additions & 25 deletions gap/projective/constructive_recognition/utils/achieve.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -364,7 +364,7 @@ RECOG.RecogniseSL2NaturalEvenChar := function(g,f,torig)

ch := Factors(CharacteristicPolynomial(f,f,t,1));
if Length(ch) <> 2 or ch[1] <> ch[2] then
Error("matrix is not triagonalizable - this should never happen!");
ErrorNoReturn("matrix is not triagonalizable - this should never happen!");
fi;

one := OneMutable(t);
Expand Down Expand Up @@ -401,12 +401,12 @@ RECOG.RecogniseSL2NaturalEvenChar := function(g,f,torig)
xm := o[j];
j := j + 1;
c := Comm(tm,xm);
until not(IsOne(c^2));
until not IsOne(c^2);
xm := xm * c^(((q-1)*(q+1)-1)/2);
x := StripMemory(xm);
xb := bas*x*bas^-1;
co := Coefficients(can,xb[2,1]);
until not(IsContainedInSpan(mb,co));
until not IsContainedInSpan(mb,co);
CloseMutableBasis(mb,co);
Add(tt,x);
Add(ttm,xm);
Expand Down Expand Up @@ -440,20 +440,20 @@ RECOG.RecogniseSL2NaturalEvenChar := function(g,f,torig)
xm := o[j];
j := j + 1;
x := MutableCopyMat(bas*StripMemory(xm)*bas^-1);
until not(IsZero(x[1,2]));
until not IsZero(x[1,2]);

if not(IsOne(x[2,2])) then
if not IsOne(x[2,2]) then
el := (One(f)-x[2,2])/x[1,2];
co := Coefficients(can,el) * mati;
for i in [1..Length(co)] do
if not(IsZero(co[i])) then
if not IsZero(co[i]) then
xm := ttm[i] * xm;
fi;
od;
x[2] := x[2] + x[1] * el;
if x <> bas*StripMemory(xm)*bas^-1 then
# FIXME: sometimes triggered by RecognizeGroup(GL(2,16));
Error("!!!");
ErrorNoReturn("!!!");
fi;
fi;
# now x[2,2] is equal to One(f)
Expand All @@ -465,7 +465,7 @@ RECOG.RecogniseSL2NaturalEvenChar := function(g,f,torig)
el := x[2,1];
co2 := Coefficients(can,el) * mati;
for i in [1..Length(co2)] do
if not(IsZero(co2[i])) then
if not IsZero(co2[i]) then
xm := xm * ttm[i];
fi;
od;
Expand Down Expand Up @@ -510,7 +510,9 @@ RECOG.GuessProjSL2ElmOrder := function(x,f)
fi;
if p > 2 then
y := x^p;
if IsOneProjective(y) then return p; fi;
if IsOneProjective(y) then
return p;
fi;
fi;
if IsOneProjective(x^(q-1)) then
facts := Collected(FactInt(q-1:cheap)[1]);
Expand All @@ -528,7 +530,7 @@ RECOG.GuessProjSL2ElmOrder := function(x,f)
j := p[2]-1;
while j >= 0 do
z := y^(s/p[1]^(p[2]-j));
if not(IsOneProjective(z)) then break; fi;
if not IsOneProjective(z) then break; fi;
j := j - 1;
od;
o := o * p[1]^(j+1);
Expand All @@ -547,24 +549,34 @@ RECOG.IsThisSL2Natural := function(gens,f)
CheckElm := function(x)
local o;
o := RECOG.GuessProjSL2ElmOrder(x,f);
if o in [1,2] then return false; fi;
if o in [1,2] then
return false;
fi;
if o > 5 then
if notA5 = false then Info(InfoRecog,4,"SL2: Group is not A5"); fi;
notA5 := true;
if seenqp1 and seenqm1 then return true; fi;
if seenqp1 and seenqm1 then
return true;
fi;
fi;
if o = p or o <= 5 then
return false;
fi;
if o = p or o <= 5 then return false; fi;
if (q+1) mod o = 0 then
if not(seenqp1) then
if not seenqp1 then
Info(InfoRecog,4,"SL2: Found element of order dividing q+1.");
seenqp1 := true;
if seenqm1 and notA5 then return true; fi;
if seenqm1 and notA5 then
return true;
fi;
fi;
else
if not(seenqm1) then
if not seenqm1 then
Info(InfoRecog,4,"SL2: Found element of order dividing q-1.");
seenqm1 := true;
if seenqp1 and notA5 then return true; fi;
if seenqp1 and notA5 then
return true;
fi;
fi;
fi;
return false;
Expand Down Expand Up @@ -594,7 +606,9 @@ RECOG.IsThisSL2Natural := function(gens,f)
notA5 := false;

for i in [1..Length(gens)] do
if CheckElm(gens[i]) then return true; fi;
if CheckElm(gens[i]) then
return true;
fi;
od;
CheckElm(gens[1]*gens[2]);
if Length(gens) >= 3 then
Expand All @@ -610,7 +624,9 @@ RECOG.IsThisSL2Natural := function(gens,f)
for i in [1..l-1] do
for j in [i+1..l] do
x := Comm(gens[i],gens[j]);
if CheckElm(x) then return true; fi;
if CheckElm(x) then
return true;
fi;
Add(coms,x);
od;
od;
Expand All @@ -620,7 +636,9 @@ RECOG.IsThisSL2Natural := function(gens,f)
a := RECOG.RandomSubproduct(gens,rec());
b := RECOG.RandomSubproduct(gens,rec());
x := Comm(a,b);
if CheckElm(x) then return true; fi;
if CheckElm(x) then
return true;
fi;
Add(coms,x);
od;
fi;
Expand All @@ -631,7 +649,9 @@ RECOG.IsThisSL2Natural := function(gens,f)
Info(InfoRecog,4,"SL2: Computing normal closure...");
clos := FastNormalClosure(gens,coms,5);
for i in [Length(coms)+1..Length(clos)] do
if CheckElm(clos[i]) then return true; fi;
if CheckElm(clos[i]) then
return true;
fi;
od;
if ForAll(clos{[Length(coms)+1..Length(clos)]},
c->RECOG.IsScalarMat(c) <> false) then
Expand Down Expand Up @@ -851,10 +871,10 @@ function(ri, g)
Info(InfoRecog,2,"ClassicalNatural: this is PSL_2!");
if IsEvenInt(q) then
std := RECOG.RecogniseSL2NaturalEvenChar(gm,f,false);
ri!.comment := "_PSL2Even";
ri!.comment := "PSL2Even";
else
std := RECOG.RecogniseSL2NaturalOddCharUsingBSGS(gm,f);
ri!.comment := "_PSL2Odd";
ri!.comment := "PSL2Odd";
fi;
Setslptonice(ri,SLPOfElms(std.all));
ri!.nicebas := std.bas;
Expand All @@ -875,7 +895,7 @@ function(ri, g)
# FIXME: Note d=3 currently has a problem in the SL2-finder.
Info(InfoRecog,2,"Classical natural: SL(",d,",",q,"): small ",
"case, handing over to Schreier-Sims.");
ri!.comment := Concatenation("_SL(",String(d),",",String(q),")",
ri!.comment := Concatenation("SL(",String(d),",",String(q),")",
"_StabilizerChain");
return FindHomMethodsProjective.StabilizerChainProj(ri,g);
fi;
Expand All @@ -890,7 +910,7 @@ function(ri, g)
x->std.basi*x*std.bas));
ri!.fakegens := RECOG.InitSLfake(f,d);
ri!.fakegens.count := 0;
ri!.comment := "_PSLd";
ri!.comment := "PSLd";
ri!.gcd := gcd;
SetFilterObj(ri,IsLeaf);
SetSize(ri,Product([0..d-1],i->(q^d-q^i))/((q-1)*gcd.gcd));
Expand Down

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